An electronic circuit of the SOC type is generally capable of executing various functions, for example, audio and/or video functions within a mobile telephone. Generally, all the functions that can be executed by the electronic circuit of the SOC type are not executed simultaneously.
A circuit of the SOC type comprises several sectors. A sector is consequently a part of the SOC circuit and may comprise one or more blocks of components.
A sector is capable of executing one or more functions and a function may be executed by one or more sectors. However, in general, a function is equivalent to a sector.
When a function is not currently being executed, it is particularly advantageous to isolate the power supply to the circuit, and the sector or sectors associated with this function, in order to reduce the leakage currents in the OFF state of the corresponding sector or sectors.
With this in mind, the power supply to a sector of such an electronic circuit is implemented by means of one or more chains of switches, for example PMOS transistors, connected to a power supply line designed to be connected to a power supply voltage VDDO for example. When the switches are closed, in other words when the transistors are conducting, the sector is electrically powered. On the other hand, when the switches are open, in other words when the transistors are turned off, the sector is isolated from the power supply line.
A control circuit, placed at the end of the chain, manages the control of the switches in such a manner as to isolate or apply a voltage to the sector in question.
When a sector is to be activated following an inactive phase, its electrical power-up requires the closure of all the switches associated with this sector. Then, when all the switches are closed, the control circuit generally generates a state signal indicating that the sector in question is correctly powered with the correct voltage. The sector can then begin to carry out its function.
At the present time, in order to cause the closing of all the switches, the control circuit delivers a control signal to the gate of the first switch of the chain and this control signal propagates along the chain so as to successively control all the switches of the chain. The control circuit then tests the level of the gate voltage of the first transistor forming the first switch, and when this voltage, which depends on the real gate voltage of all the transistors (switches), is lower (when the switches are PMOS transistors) than a given threshold, and the control circuit delivers the state signal.
However, when the size of a sector, and consequently the length of the switch chains designed to power this sector is very long, typically greater than 10 mm, the state signal is delivered while one or more switches situated at the end of the chain have still not switched from their open state to their closed state.